Our recent discovery of methods whereby reversible heme oxygenation kinetics and equilibria can be studied in almost any environment upon oxygenation. We propose to explore in detail the kinetics of reversible complexation of isolated heme protein sites with all the ligands which have shown binding to myoglobin and hemoglobin. The effects of solvent, of immobilization, pH, proximal basicity and distal groups upon reversible oxygenation will also be studied. Through these studies we hope to define precisely the local environmental conditions which affect oxygenation and to understand the cooperativity in hemoglobin oxygenation as well as the differences in oxygen affinity among heme proteins.